1. Field of the Invention
The invention relates to the use of mixed hydroxyethers of the general formula I EQU R.sup.1 O--(CH.sub.2 CH.sub.2 O).sub.x --CH.sub.2 -CH(OH)R.sup.2 (I)
in which
R.sup.1 denotes an alkyl group having 1 to 10 carbon atoms,
R.sup.2 denotes an alkyl group having 8 to 20 carbon atoms and x denotes a number in the range from 1 to 20 as auxiliaries for the dehydration of water-containing finely divided solids.
2. Discussion of Related Art
In many branches of industry, e.g. in mining or in sewage treatment plants, large amounts of finely divided solids having high water contents, which have to be dehydrated before further processing of the solids or their disposal, are formed. Thus, for example, the dehydration of water-containing coal or coke is a central process in the processing of fuels based on coal. The maximum allowable values for the water content of these materials demanded by the market can often be adhered to only with difficulty, since, for example, the coal supplied is produced in very fine particles due to the extensive mechanization of the underground coal mining. Currently, about 38% of the run-of-mine coal is fines having a particle diameter in the range from 0.5 to 10 mm; a further 14% is duff having a particle diameter below that.
It is known to use surfactants as dehydration auxiliaries for the dehydration of water-containing finely divided solids, in particular coals, which make it possible to reduce the residual moisture of fines and duff. This is explained by the property of the surfactant to reduce the surface tension and the capillary pressure of water in the material to be extracted. At the same time, this reduces the adhesive energy which must be supplied to remove the surface water. This leads to improved dehydration, when surfactants are used, while the amount of energy remains unchanged.
Dialkyl sulfosuccinates (U.S. Pat. No. 2,266,954) and nonionic surfactants of the type of alkylphenol polyglycol ethers [Erzmetall 30, 292 (1977)] have been described as surfactant-based dehydrating auxiliaries of the above-mentioned types. However, these surfactants have the disadvantage of showing excessive foaming, which leads to considerable problems in the processing plants, in particular in the recirculation of the water which is usually employed.